The proposed research will investigate the role of relevant islet cell autoantibody, HLA markers, and a novel potential IDDM susceptibility genetic locus (polymorphism of the gene ICA1), in the largest population-based cohort of relatives, with and without IDDM, from the same geographical area. Small sample sizes, limited follow-up and the lack of advanced technology have limited previous studies in this field. For the first time, it will be possible to determine the risk of conversion to IDDM utilizing new islet autoantibody assays and compare with that estimated by the old cytoplasmic ICA assay in this specific population. Over the past few years, molecular biology techniques have been applied and a diabetes-related 69 kDa peptide autoantigen named Islet Cell Autoantigen 69 kDa (ICA69) and the novel antigen ICA12 were identified. Presently, recent data indicate that the two most popular biochemical assays for detecting autoantibodies to GAD65 and IA-2 are not sufficient for predicting IDDM. The proposed project plans to optimize biochemical assays for detecting autoantibodies reacting with the following human islet autoantigens: GAD65, IA-2, insulin, ICA69 and ICA12. These 5 recombinant autoantigens are accessible for antibody screening. This research will be performed at the Pittsburgh center which currently has 78 relatives, who converted to IDDM during a prospective follow-up (converters), from a pool of over 5,500 relatives. Approximately 100 converters will be available by the end of this grant period. This represents the largest number of convertors for any center. Also, DNA has been collected from relatives of IDDM patients, and we have specimens on complete simplex and multiplex families with diabetic and unaffected siblings in our repository. This is a unique set of serum and DNA samples for the testing of immunologic and genetical hypotheses. The outcome of the proposed investigation should facilitate the stage for the application of antibody and HLA-DQ and -DR markers in the screening for IDDM in the general population and for risk assessment for IDDM in intervention trials intended to prevent IDDM.